i 4 2 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



its activity. If the spinal cord of a young salamander 

 be severed the swimming movements of the anterior 

 and posterior parts are so well coordinated that it 

 hardly seems credible that an operation has been per- 

 formed. The same is true of the eel (8). The con- 

 ditions are about the same as in the earthworm. 



Rubbing the back of the frog causes it to croak, and 

 in a frog whose brain has been removed as far as 

 the medulla oblonerata. this sound, as Goltz has 



o 



found, can be produced with machine-like regularity 

 (2). Viewed from the segmental standpoint this reflex 

 is naturally conditioned by the integrity of the me- 

 dulla, since it is there that the motor nerves for the 

 production of the voice originate. The centre-theory 

 had found a supposed " centre " for this reflex higher 

 up in the brain. 



4. The instinct for food and self-preservation was, 

 like all the instincts, located in the cerebral hemi- 

 spheres. An analysis of this instinct shows that it is 

 composed of several reflexes, which are discharged 

 successively. The first is a visual reflex ; the frog 

 catches only objects (flies, for instance) that are in 

 motion. The opticus ends in the thalamus opticus, 

 hence it is to be expected that the loss of the cerebral 

 hemispheres would not prevent the frog from catch- 

 ing flies. Schrader found this to be the case. If 

 previous authors believed their experiments to prove 

 that the cerebral hemispheres are necessary for see- 

 ing, they were misled by the shock-effects of the 

 operation, and in this way made the localisation too 



